Many different types of systems and methods have previously been used to deform heated glass sheets from a flat shape to a curved shape. For example, vehicle windshields, side windows, and back windows are conventionally manufactured by heating flat glass sheets and then deforming the glass sheets to the desired curvature for the particular vehicle windshield or window involved. Also, presently there is an increasing use of curved architectural glass.
Different terminology has been utilized in the past to refer to deformation of flat glass sheets to a curved shape. The terms forming, bending, and shaping are all utilized to refer to such deformation of glass sheets whether the finally curved shape is relatively shallow and easy to perform, relatively deep or abrupt and harder to perform, or relatively complex and hard to perform even if not particularly abrupt or deep. Complex bends are glass shapes that have both concave and convex curvatures on each surface of the glass sheet and may also include deep and/or abrupt bends. Such complex bends are becoming increasingly difficult to manufacture with conventional forming methods and systems.
U.S. Pat. Nos. 4,282,026, 4,437,871, and 4,437,872 of Harold A. McMaster, Norman C. Nitschke, and John S. Nitschke disclose a system for bending heated flat glass sheets relatively quickly to a curved shape under the force of gravity. This system includes a holder having a downwardly facing surface that receives a heated glass sheet from a horizontal conveyor on which heating takes place. The holder then supports the heated glass sheet above the conveyor in preparation for bending. A curved bending mold of the system is positioned under the holder and has at least a substantial portion with a greater curvature than the holder surface. The mold then receives the heated glass sheet from the holder for bending under the force of gravity. One preferred embodiment of the system utilizes a planar holder surface such that only the curved mold must be changed when different sizes and/or shapes of glass sheets are to be bent. Another preferred embodiment disclosed for making relatively deep bends includes a curved holder surface against which the planar heated glass sheet received from the conveyor is pre-bent prior to gravity deformation below the curved holder on the curved mold which has a greater curvature than that of the curved holder surface.
U.S. Pat. No. 4,233,049 discloses another system for bending heated, flat glass sheets by releasing the glass sheets from a flat platen onto a curved bending mold for bending.
U.S. Pat. No. 4,260,408 discloses a glass sheet forming system wherein an initial bending operation and a subsequent press forming operation between a pair of opposed molds both take place at the same station.
U.S. Pat. No. 4,356,018 of Harold A. McMaster discloses a method and apparatus for deep bending glass sheets by initially releasing one portion thereof from a downwardly facing surface onto a curved bending mold while retaining another portion of the glass sheet against the downwardly facing surface by an upward flow of gas. Termination of the upward gas flow releases the other portion of the glass sheet in a manner that permits bending of the glass sheet to the curved shaped of the mold without substantial sliding between the glass sheet and the mold.
Vehicle windshields are conventionally made by supporting a pair of glass sheets on a curved mold that is passed through an elongated furnace for slow sagging of the glass sheets to the mold shape. Thereafter, the curved glass sheets are laminated to each other by an intermediate layer of plastic in order to hold the glass in position upon breakage.
Most glass sheet bending and forming is performed with open center ring type molds or full surface molds. Open center ring type molds engage only the periphery of the glass sheet being deformed and thus prevent the possibility of any marking of the center glass area and resultant loss in optical quality. Full surface molds engage the center as well as the periphery of each glass sheet being deformed and thereby provide a more accurate control of the final shape of the center of the glass sheet.